I'm looking to imitate ShareX's behaviour in Gnome. I want the screen to freeze before I take a regional screenshot. It would also be nice to get other features of ShareX too, however, I'm not sure if that's easily achievable.
KDE has an awesome screenshot tool that does exactly what I want called "Spectacle". It works (perhaps surprisingly) well on Gnome too.
To install Spectacle:
sudo apt install kde-spectacle